Numerous geometric configurations of reflectors and filters employing various shape conic sections have been designed into illumination systems for reflecting and filtering light rays. Generally, in illumination systems used in xerographic reproducing apparatus, or other electrophotographic systems, it is desired to focus the visible spectrum produced by a light source onto a document scan station after filtering out the infra-red (IR) spectrum and directing those rays to a heat sink. In these prior art systems so-called hot mirrors are widely used and are effective for transmitting the visible spectrum while reflecting the infra-red rays. Cold mirrors which transmit IR while reflecting the visible spectrum are also used, and are preferable to hot mirrors since they usually produce a more efficient heat/light separation. However, both cold and hot mirror systems as known in the prior art have been designed to take the separated infra-red spectrum and direct it to a heat sink, and therefore that portion of the energy consumed by the light source going into the production of IR is wasted. It is, therefore, the general object of this invention to utilize the infra-red rays for useful purposes and thereby produce a more efficient illumination system. It is a more specific object of this invention to increase the efficiency of the illumination system by reflecting the infra-red spectrum onto the filament and thereby either decrease the amount of electrical energy needed to heat the filament or to produce a hotter filament.
In electrophotographic reproducing equipment, a focused line of light is passed from one end of a document scanning station to another. To achieve the movement of a line of light, many reproducing machines use a traveling carriage which supports the illumination system. It is another object of this invention that the heat produced by the light source be kept away from those components of the carriage which tend to warp from heat, resulting in carriage travel problems.
Tungsten-halogen lamps, a variety of incandescent lamps, are often used in electrophotographic reproducing apparatus. It is well known that the purpose of adding a halogen gas to the interior of a tungsten filament bulb is to maintain the illumination intensity of the filament over its entire life by preventing buildup of tungsten on the bulb wall. That is accomplished by the formation of a halogentungsten combination near or at the bulb wall thereby preventing the undesirable deposition of tungsten on the wall. However, in order for that combination to occur, it is necessary to heat the bulb wall above halogen temperature, which in the case of the halogen, bromine, is in the neighborhood of 200 degrees Celsius. It is, therefore, a further object of this invention to reflect infra-red heat generated by the light source back to the light source for the purpose of heating the bulb wall to aid in maintaining the temperature of the bulb wall above halogen temperature.